Reactor system for conversion of alcohols to ether-rich gasoline

ABSTRACT

Methanol or other alcohol is converted to high octane gasoline components in an integrated apparatus wherein crude aqueous alcohol feedstock is extracted with a liquid extractant stream containing C 4  + iso-olefin and reacted to form tertiary-alkyl ethers, such as MTBE. The aqueous raffinate is converted to olefinic hydrocarbons in a MTO catalytic reactor. Propene from the MTO reaction is reacted with water to produce di-isopropyl ether, which may be blended with MTBE and C 6  +MTO hydrocarbons to produce high octane gasoline. Isobutylene and isoamylenes from the MTO reaction can be recovered and recycled as a liquid extractant stream.

This is a division of application Ser. No. 344,585, filed on Apr. 28,1989, now U.S. Pat. No. 5,041,690.

BACKGROUND OF THE INVENTION

This invention relates to techniques for converting crude methanol orother C₁ -C₄ lower aliphatic alcohols to alkyl tertiary-alkyl ethers,di-isopropyl ether (DIPE), and gasoline range hydrocarbons. Inparticular, this invention relates to an integrated system forconverting crude methanol to valuable products by etherifying lowerbranched olefins, such as C₄ -C₇ normally liquid iso-olefins. It isknown that isobutylene and other isoalkenes produced by hydrocarboncracking may be reacted with methanol over an acidic catalyst to providemethyl tertiary butyl ether (MTBE) and isoamylenes may be reacted withmethanol over an acidic catalyst to produce tertiary-amyl methyl ether(TAME). Those ethers having the formula CH₃ --O--R, where R is atertiary alkyl radical, are particularly useful as octane improvers forliquid fuels, especially gasoline.

MTBE and TAME are known to be high octane ethers. The article by J.D.Chase, et al., Oil and Gas Journal, Apr. 9, 1979, discusses theadvantages one can achieve by using these materials to enhance gasolineoctane. The octane blending number of MTBE when 10% is added to a basefuel (R+O=91) is about 120. For a fuel with a low motor rating (M+O=83)octane, the blending value of MTBE at the 10% level is about 103. On theother hand, for an (R+O) of 95 octane fuel, the blending value of 10%MTBE is about 114.

Increasing demand for high octane gasoline blended with lower aliphaticalkyl ethers as octane boosters and supplementary fuels has created asignificant demand for isoalkylethers, especially the C₅ to C₇ methylalkyl ethers, such as methyl tertiary butyl ether (MTBE) and tertiaryamyl methyl ether (TAME). Methanol may be readily obtained from coal bygasification to synthesis gas and conversion of the synthesis gas tomethanol by well-established industrial processes. As an alternative,the methanol may be obtained from natural gas by other conventionalprocesses, such as steam reforming or partial oxidation to make theintermediate syngas. Crude methanol from such processes usually containsa significant amount of water, usually in the range of 4 to 20 wt %;however, the present invention is useful for removing water in lesseramounts or greater.

It is main object of the present invention to provide a novel andeconomic technique for removing excess water from crude methanolfeedstocks, including novel operating methods and equipment for treatingthese oxygenate feedstocks prior to etherification and disposing ofraffinate containing methanol. It has been discovered that aqueousmethanol streams, such as etherification feedstock extraction byproductcan be economically upgraded by catalytic conversion concurrently withhydrocarbons.

SUMMARY OF THE INVENTION

A continuous technique has been found for converting crude methanol tohigh octane gasoline and mixed ethers. A process is provided forconverting crude aqueous alcohol feedstock to tertiary-butyl ether andtertiary-amyl methyl product in contact with acid catalyst comprisingthe steps of: contacting the aqueous alcohol feedstock with liquidhydrocarbon extractant comprising C₄ -C₅ mixed olefinic hydrocarbonscomprising isobutylene and isoamylenes under liquid extractionconditions; recovering an aqueous raffinate phase containing alcohol anda major amount of water introduced with the feedstock; recovering anorganic extract phase comprising the hydrocarbon extractant and aportion of alcohol introduced in the feedstock sufficient to etherify amajor amount of tertiary olefins in the extract phase; and catalyticallyconverting alcohol in the raffinate phase to predominantly lower olefinsrich in propene and isoalkene hydrocarbons, reacting extracted alcoholwith the isobutylene and isoamylenes under catalytic etherificationreaction conditions to produce predominantly C₅ + t-alkyl ethers.Isoalkenes produced by catalytic conversion of alcohol can be recoveredin a C₄ -C₅ liquid stream, containing butenes, amylenes or mixturesthereof, and employed as liquid extractant. By reacting propenerecovered from alcohol conversion with water to produce di-isopropylether, an additional octane booster ether product is obtained.

A significant process improvement is provided wherein byproductisopropanol is coproduced with di-isopropyl ether by reaction of propenewith water. The isopropanol may be converted to hydrocarbonsconcurrently with raffinate alcohol, or at least a portion of thebyproduct isopropanol, di-isopropyl ether and tertiary-alkyl ether maybe blended with liquid C₆ + hydrocarbons to produce high octane gasolineproduct.

It is a particular object of this invention to provide a process usefulfor converting feedstock containing methanol and about 2 to 20 wt %water. A typical t-alkyl ether catalyst is sulfonic acid resin or otheracid, such as aluminasilicate zeolites, etc. In the secondary effuentconversion stage, the methanol is converted to olefinic hydrocarbonsadvantageously with a medium pore shape selective metallosilicatecatalyst, such as ZSM-5 zeolite. These and other objects and features ofthe invention will be understood from the following description and inthe drawings.

DRAWINGS

FIG. 1 of the drawings is a schematic etherification process flowsheetdepicting the present invention;

FIG. 2 is a typical fluidized bed reactor system adaptable forconversion of methanol.

DETAILED DESCRIPTION

Typical feedstock materials for etherification reactions crude methanolcommercially available from syngas processes, which may contain up to 30wt % water, which must be removed, preferrably to a methanol purity ofabout 99.8 wt %. It has been found that more than 75% of crude feedstockmethanol can be recovered by liquid extraction with light olefinicliquid extractant, such as butenes and C₅ + light olefinic naphtha. Thetypical hydrocarbon feed ratio range is about 2 to 8 parts per part byweight of extracted methanol.

Typical processing equipment operatively connected according to thepresent invention includes a continuous feedstock separation andetherification reactor system for converting crude methanol oxygenatefeedstock and iso-olefin to methyl t-alkyl ether, wherein the unitoperation apparatus includes: extractor means for contacting crudefeedstock liquid containing a minor amount of water with a liquidhydrocarbon extraction stream under extraction conditions favorable toselective extraction of methanol, thereby providing an extract liquidstream containing sufficient methanol for etherification and an aqueousraffinate stream lean in methanol; first catalytic reactor meansoperatively connected for contacting the extract stream in a catalyticreaction zone with acid etherification catalyst in an etherificationreaction zone under process conditions to convert a major portion ofmethanol to ether; second catalytic reactor means for contacting saidraffinate stream with methanol conversion catalyst in the presence ofhydrocarbon to produce olefinic hydrocarbons; means for charging atleast a portion of said olefinic hydrocarbon rich in C₄ -C₅ iso-olefinliquid from said second reactor means to said extractor means as saidextraction stream; means for separating water and a propylene-rich C₃stream from said second reactor means; and third reactor means forcontacting said propylene-rich C₃ stream with water under etherificationconditions with a solid catalyst to produce di-isopropyl ether.

Referring to FIG. 1 of the drawing, a continuous stream of crudemethanol (MeOH) feedstock is introduced via conduit 10 with a stream ofC₄ + olefinic hydrocarbon liquid extractant introduced via conduit 12 toa top inlet of extraction separation unit 14, operated at about 35°-40°C. The fluid handling system includes flow control valve means FCVresponsive to flow sensors F1 for conduits 12 and 18. These streams arecontacted under liquid extraction conditions to provide an aqueousraffinate phase. An aqueous stream containing a major amount of thewater present in the crude feedstock is withdrawn via conduit 16. Thelighter organic extract phase containing hydrocarbon extraction solventand the major amount of feedstock methanol is recovered from extractionunit 14 via conduit 18, and introduced under temperature and processconditions suitable for conversion of methanol in contact withetherification catalyst in a first reactor unit 30. From reactor 30, theeffluent product stream passes to a debutanizer or fractionation tower(not shown), where the C₅ + methyl tert-alkyl ether product is recoveredas a liquid stream 32, along with unreacted C₅ + hydrocarbons in theextractant. Tower overhead comprising unreacted C₄ + hydrocarbons andmethanol are recovered by line 34.

The aqueous raffinate stream 16 consists essentially of water,partitioned methanol (50-80 wt %) and a trace of hydrocarbon. Thisstream is reactive at elevated temperature in the presence of an acidzeolite catalyst, such as medium pore shape selective zeolite, such as,ZSM-5, etc., in a MTO conversion unit 40, typically a fluidized bedreaction zone. Optionally, the aqueous methanol raffinate stream may becoreacted with unextracted feedstream 19, which bypasses the flowcontrol valve FCV associated with etherification reactant flow. Olefiniclight gas and/or other reactive hydrocarbon feedstreams may also beconverted in a methanol-to. olefins (`MTO`) reaction section, asdescribed by Owen et al in U.S. Pat. No. 4,746,762. The aqueous methanolmay be introduced as a liquid directly to the reaction zone (bottom ormiddle section), as herein described with regard to FIG. 2, or vaporizedand mixed with diluent and/or supplemental hydrocarbon feed.

The propene-rich C₃ Stream 42 and stream 44 containing a portion ofbyproduct water from the MTO unit 40 are contacted with an acidetherification catalyst in DIPE unit 50 to produce di-isopropyl ether,which may be recovered by conventional fractionation to provide productsteam 54 and unreacted C3's. Byproduct isopropanol may be recovered asproduct stream 52 or fed to be converted in MTO or MTBE (methyl t-butylether) to produce additional hydrocarbons or ethers.

Extraction Unit Operation

Although the alcohol feedstock may comprise one or more C₁ -C₄ loweraliphatic alkanols, the preferred crude material is methanol containingabout 2 to 20%, preferrably 4 to 17% by weight water. The extractioncontact unit may be a stirred multi-stage vertical extraction columnadapted for continuous operation at elevated pressure. Any suitableextraction equipment may be employed, including cocurrent, cross-currentor single contactors, wherein the liquid methanol feedstock isintimately contacted with a substantially immiscible liquid hydrocarbonsolvent, which may be a mixture of C₄ + aliphatic components includinglower alkanes, n-alkenes or relatively pure isoalkenes, such asisobutylene, etc. This unit operation is described in Kirk-OthmerEncyclopedia of Chemical Technology (Third Ed.), 1980, pp. 672-721.Other equipment for extraction is disclosed in U.S. Pat. Nos. 4,349,415(DeFilipi et al), 4,626,415 (Tabak), and 4,665,237 (Arakawa et al). Unitoperation details are also disclosed by Harandi et al in U.S. Pat. No.4,777,321 and in copending U.S. patent application Ser. No. 179,726,filed Apr. 11, 1988, incorporated herein by reference. The methanolextraction step can be performed advantageously in a countercurrentmultistage design, such as a simple packed column, rotating disk column,agitated column with baffles or mesh, or a series of single stage mixersand settlers.

Tertiary Ether Production

The reaction of methanol with isobutylene and isoamylenes at moderateconditions with a resin catalyst is known technology, as provided by R.W. Reynolds, et al., The Oil and Gas Journal, June 16, 1975, and S.Pecci and T. Floris, Hydrocarbon Processing, December 1977. An articleentitled "MTBE and TAME - A Good Octane Boosting Combo", by J. D. Chase,et al., The Oil and Gas Journal, Apr. 9, 1979, pages 149-152, discussesthe technology. A preferred catalyst is a polysulfonic acid resin, suchas "Amberlyst 15" resin.

Processes for producing and recovering MTBE and other methyl tert-alkylethers for C₄ -C₇ isoolefins are known to those skilled in the art, suchas disclosed in U.S. Pat. Nos. 4,544,776 (Osterburg et al) and 4,603,225(Colaianne et al). Various suitable extraction and distillationtechniques are known for recovering ether and hydrocarbon streams frometherication effluent.

MTO Conversion of Methanol to Hydrocarbons

Zeolite catalysis technology for upgrading lower aliphatic hydrocarbonsand oxygenates to lower olefins and liquid hydrocarbon products are wellknown. Commerial Methanol-to-Gasoline (MTG), methanol-to olefins (MTO)and Mobil Olefin to Gasoline/Distillate (MOG/D) processes employ shapeselective medium pore zeolite catalysts for these processes. It isunderstood that the present zeolite conversion unit operation can havethe characteristics of these catalysts and processes to produce avariety of hydrocarbon products, especially C₃ -C₅ olefins, and liquidaliphatic and aromatics in the C₆ -C₉ gasoline range.

Description of Zeolite Catalysts

Recent developments in zeolite technology have provided a group ofmedium pore siliceous materials having similar pore geometry. Mostprominent among these intermediate pore size zeolites is ZSM-5, which isusually synthesized with Bronsted acid active sites by incorporating atetrahedrally coordinated metal, such as Al, Ga, Fe or mixtures thereof,within the zeolitic framework. These medium pore zeolites are favoredfor acid catalysis; however, the advantages of ZSM-5 structures may beutilized by employing highly siliceous materials or crystallinemetallosilicate having one or more tetrahedral species having varyingdegrees of acidity. ZSM-5 crystalline structure is readily recognized byits X-ray diffraction pattern, which is described in U.S. Pat. No.3,702,866 (Argauer, et al.), incorporated by reference.

Zeolite hydrocarbon upgrading catalysts preferred for use herein includethe medium pore (i.e., about 5-7A) shape-selective crystallinealuminosilicate zeolites having a silica-to-alumina ratio of at least12, a constraint index of about 1 to 12 and acid cracking activity(alpha value) of about 1-250, preferably about 3 to 80 based on totalcatalyst weight. In the fluidized bed reactor the coked catalyst mayhave an apparent activity (alpha value) of about 3 to 80 under theprocess conditions to achieve the required degree of reaction severity.Representative of the ZSM-5 type medium pore shape selective zeolitesare ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, and ZSM-48.

Aluminosilicate ZSM-5 is disclosed in U.S. Pat. No. 3,702,886 and U.S.Pat. No. Re. 29,948. Other suitable zeolites are disclosed in U.S. Pat.Nos. 3,709,979; 3,832,449; 4,076,979; 3,832,449; 4,076,842; 4,016,245;4,414,423; 4,417,086; 4,517,396 and 4,542,251, incorporated herein byreference. While suitable zeolites having a coordinated metal oxide tosilica molar ratio of 20:1 to 200:1 or higher may be used, it isadvantageous to employ a standard ZSM-5 having a silica alumina molarratio of about 25:1 to 70:1, suitably modified if desired to adjustacidity.

Certain of the ZSM-5 type medium pore shape selective catalysts aresometimes known as pentasils. In addition to the preferredaluminosilicates, the gallosilicate, and ferrosilicate materials may beemployed. ZSM-5 type pentasil zeolites are particularly useful in theprocess because of their regenerability, long life and stability underthe extreme conditions of operation. Usually the zeolite crystals have acrystal size from about 0.01 to 2 microns or more. In order to obtainthe desired particle size for fluidization in the turbulent regime, thezeolite catalyst crystals are bound with a suitable inorganic oxide,such as silica, alumina, etc. to provide a zeolite concentration ofabout 5 to 95 wt %. It is advantageous to employ a standard ZSM-5 havinga silica:alumina molar ratio of 25:1 or greater in a once-throughfluidized bed unit to convert 60 to 100 percent, preferably at least 75wt %, of the monoalkenes and methanol in a single pass. In the preferredembodiment 25% H-ZSM-5 catalyst calcined with 75% silica-alumina matrixbinder is employed unless otherwise stated.

Fluidized Bed Reactor Operation

Suitable feedstreams to the methanol conversion unit comprise variousalcohols, such as methanol and, optionally, isopropanol obtained fromthe DIPE etherification operation. The reaction severity conditions canbe controlled to optimize yield of the desired olefins, gasoline or C₆-C₈ BTX (benzene/toluene/-eyelenes) hydrocarbons, according to productdemand by providing either fresh or regenerated catalyst having thedesired properties. Reaction temperatures and contact time are alsosignificant factors in the reaction severity, and the process parametersare followed to give a substantially steady state condition wherein thereaction severity is maintained within the limits which yield a desiredweight ratio of propane to propene in the reaction effluent.

In a turbulent fluidized catalyst bed the conversion reactions areconducted in a vertical reactor column by passing hot reactant vaporupwardly through the reaction zone at a velocity greater than dense bedtransition velocity and less than transport velocity for the averagecatalyst particle. A continuous process is operated by withdrawing aportion of coked catalyst from the reaction zone, oxidativelyregenerating the withdrawn catalyst and returning regenerated catalystto the reaction zone at a rate to control catalyst activity and reactionseverity to effect feedstock conversion. In a typical process, themethanol and olefinic feedstream is converted in a catalytic reactorunder moderate pressure (i.e.-100 to 2500 kPa).

Referring now to FIG. 2, liquid methanol-containing raffinate 16 fromthe extractor is passed under pressure via feed conduit 116 forinjection into vertical reactor vessel 110 above a feed distributor grid112, which provides for distribution of hot vapor feed passing viaconduit 114 through the small diameter holes in the grid 112.Fluidization is effected in the bottom portion of the bed by upwardlyflowing gas introduced via conduit 114, which may be supplemented withadditional reactive gas 114A, such as ethylenic fuel gas or the like.Thermodynamic conditions in the reaction vessel can be controlled byadjusting liquid injection rate, vapor feed temperature, catalysttemperature and rate, or by heat exchange means 115.

Provision is made for withdrawing catalyst from above grid 112 byconduit means 117 provided with flow control valve means to controlpassage via air lift line 118 to the catalyst regeneration system invessel 120 where coked catalyst particles are oxidatively regenerated incontact with air or other regeneration gas at high temperature.Regenerated catalyst is returned to the reactor fluid bed 110 throughconduit means 122 provided with flow control valve means. The hotregenerated catalyst is charged to the catalyst bed sufficiently belowthe upper interface to achieve good mixing in the fluid bed.

The product effluent separated from catalyst particles in the cycloneseparating system then passes to effluent separation system 130. Theproduct effluent is cooled and separated to recover a propene-rich C₃stream, C₄ -C₅ iso-olefins, C₆ + liquid gasoline range hydrocarbons,fuel gas, along with byproduct water. The preferred fluid bed reactorsystems are described in U.S. Pat. Nos. 4,547,616 (Avidan et al);4,751,338 (Harandi & Owen) ed; and in U.S. Pat. 4,579,999 (Tabak et al),incorporated herein by reference.

A typical single pass reactor unit employs a temperature controlled inthe usual operating range of about 250° C. to 650° C., preferably ataverage reactor temperature of 350° C. to 580° C., at moderate pressureof about 100 to 3000 kPa (atmospheric to about 400 psig). The weighthourly space velocity (WHSV, based on total alcohol in the feedstream)usually is about 0.1-5 WHSV.

DIPE Reaction

Olefin hydration to provide ethers and alcohols is well known. Reactionof propene with water to produce DIPE and byproduct isopropyl alcohol(IPA) is an acid catalyzed process step, as described in U.S. Pat. No.4,214,107 and 4,499,313. The preferred catalytic methods for making DIPEemploy solid acid catalysts, such as zeolites Y, Beta and/or ZSM-5aluminosilicate. DIPE etherification conditions may vary widely inchoice of temperature, pressure and reaction time. The preferred methodof Bell et al reacts propene with water in a fixed bed of zeolite Betaat about 90° to 200° C. and pressure of at least 4000 kPa. However, itis understood that the unit operations described herein can be conductedwith any number of specific process steps within the skill of the art.

The present invention is particularly advantageous in the economicdewatering of crude methanol, thus avoiding expensive andenergy-intensive prefractionation by distillation. By extractingmethanol from the crude feedstock with olefinic hydrocarbon reactantliquid, substantial utilities and equipment savings are realized.Various modifications can be made to the system, especially in thechoice of equipment and non-critical processing steps.

To demonstrate the advantages of the invention, an integratedmulti-reactor methanol conversion process according to the presentinvention is compared to a conventional prior art MTO single reactorprocess in Table 1, wherein the two continuous process flowrates aregiven in parts by weight, based on 100 parts methanol feedstock.

                  TABLE 1                                                         ______________________________________                                        Comparison of the Improved Process With MTO                                                  NET PRODUCT                                                           Crude     Prior                                                               Methanol  MTO     Improved Process                                     ______________________________________                                        C.sub.2.sup.-        4.9     4.7                                              C.sub.3 's           11.4    5.2                                              C.sub.4 's           9.6     4.5                                              C.sub.5 's           5.3     3.4                                              C.sub.6.sup.+        12.8    13.0                                             Methanol 100                                                                  MTBE                         7.5                                              TAME                         2.5                                              DIPE                         6.4                                              H.sub.2 O                                                                               10         66      62.8                                             Total    110         110     110                                              ______________________________________                                    

The improved multi-reactor process makes 81% more C₅ + fuel frommethanol than the conventional MTO process. In addition, the gasolinecontains about 50% very high octane ethers. Table 2 gives materialbalances for the three reactors, based on 100 parts methanol feed.

                                      TABLE 2                                     __________________________________________________________________________    Reactors Material Balances for Converting Methanol to Ethers                                    MTBE/ MTBE/                                                 MTO        MTO    TAME  TAME     DIPE  DIPE                                   RX FEED    PRODUCT                                                                              RX FEED                                                                             RX EFFLUENT                                                                            RX FEED                                                                             RX EFFLUENT*                           __________________________________________________________________________    C.sub.2.sup.-                                                                            4.7                                                                C.sub.3 's 11.0                  11.0  5.2                                    C.sub.4 's 9.3    9.3   4.5                                                   C.sub.5 's 5.1    5.1   3.4                                                   C.sub.6.sup.+                                                                            12.4                        0.6                                    Methanol                                                                           96.5         3.6   0.1                                                   MTBE                    7.5                                                   TAME                    2.5                                                   DIPE                                   6.43                                   H.sub.2 O                                                                          10.0  64     0.04  0.04     1.3   0.07                                   Total                                                                              106.5 106.5  18.04 18.04    12.3  12.3                                   __________________________________________________________________________     *Assuming IPA is recycled to extinction.                                 

While the invention has been described by specific examples, there is nointent to limit the inventive concept as set forth in the followingclaims.

We claim:
 1. A continuous feedstock separation and etherificationreactor system for converting crude methanol feedstock to methyl t-alkylether comprising:extractor means for contacting crude feedstock liquidcontaining a minor amount of water with a liquid olefinic hydrocarbonextraction stream under extraction conditions favorable to selectiveextraction of methanol, thereby providing an extract liquid streamcontaining a major amount of feedstock methanol and an aqueous raffinatestream lean in methanol; first catalytic reactor means operativelyconnected for contacting the extract liquid stream with acidetherification catalyst in an etherification reaction zone under processconditions to convert a major portion of methanol to ether; effluentseparation means for recovering ether product from unconverted olefinichydrocarbon and methanol; and second catalytic reactor means operativelyconnected for contacting said aqueous raffinate stream with conversioncatalyst in the presence of said unconverted olefinic hydrocarbon andmethanol to produce normally liquid C₆ + hydrocarbon product, propylenerich olefins, C₄ -C₅ olefinic hydrocarbons rich in iso-olefin, andwater; means for recovering and charging at least a portion of said C₄-C₅ olefinic hydrocarbons rich in iso-olefin from said second reactormeans to said extractor means as said liquid olefinic hydrocarbonextraction stream.
 2. A continuous reactor system for converting crudeaqueous alcohol feedstock to ether comprising:(a) extractor meansoperatively connected to receiving and contacting the crude aqueousalcohol feedstock a minor amount of water with a reactive olefinicliquid extractant stream under extraction conditions favorable toselective extraction of the alcohol, thereby providing a liquid extractstream containing alcohol with reactive olefinic liquid extractant andan aqueous raffinate stream lean in alcohol; (b) etherification reactormeans for reacting liquid hydrocarbon extractant and extracted alcoholsubstantially free of water in a first catalytic reaction zone incontact with acid etherification catalyst under etherification processconditions to convert alcohol and said reactive olefinic liquidextractant to an alkyl ether product; (c) means for fractionating theetherification effluent from step (b) to recover liquid productcontaining ether; (d) second reactor means for catalytically convertingalcohol in said aqueous raffinate stream to predominantly lower olefinsrich in propene and C₄ -C₅ olefin; (e) means for recovering effluentfrom said second reactor means in a C₄ -C₅ liquid stream for recycle asreactive olefinic liquid extractant; and (f) third reactor means forreacting propene from said second reactor means for conversion withwater to produce di-isopropyl ether.
 3. An improved feedstock extractionand etherification reactor system for converting crude aqueous alcoholfeedstock to ether product comprising:extractor means for contacting theaqueous alcohol feedstock with liquid hydrocarbon extractant comprisingC₄ -C₅ mixed olefinic hydrocarbons comprising isobutylene andisoamylenes under liquid extraction conditions; means for recovering anaqueous raffinate phase containing a portion of feedstock alcohol and amajor amount of water introduced with the feedstock; means forrecovering an organic extract phase comprising the hydrocarbonextractant and a major amount of alcohol introduced in the feedstock;alcohol conversion reactor means for catalytically converting alcohol inthe raffinate phase to predominantly lower olefins rich in propene andisoalkene hydrocarbons; and first etherification reactor means forreacting extracted alcohol with the isobutylene and isoamylenes undercatalytic etherification reaction conditions to produce predominantlyC₅ + t-alkyl ethers; and second etherification reactor means forreacting propene from alcohol conversion with water to producedi-isopropyl ether.
 4. The system of claim 3 including means forrecovering said isoalkene produced by catalytic conversion of alcohol ina C₄ -C₅ liquid stream for recycle as liquid extractant.